PATHOGENIC VARIABILITY WITHIN FUSIFORM AND EASTERN GALL RUST 50' 



The four collections of C. fusiforme. produced relatively uniform 

 infection responses on the 16 pine species (Table 2) . On very suscep- 

 tible species, such as Jefferey, Monterey, South Florida slash, and 

 ponderosa pine, infections averaged almost 80%. This indicates that all 

 species were exposed to relatively high concentrations of inoculum under 

 conditions conducive to infection. Even under these optimum conditions, 

 some species, such as loblolly, slash, and Austrian pine, had intermediate 

 infection ranging from 35 to 50%. Nine of the species were essentially 

 resistant. This latter group included such southern species as pond, 

 sand, and spruce pine. 



These results agree generally with the earlier work by Hedgcock and 

 Siggers (1949). In comparison with Hedgcock and Siggers data, our lob- 

 lolly infection was lower, the slash pine higher, and Jefferey, ponderosa, 

 and Monterey considerably higher. One of the most interesting differences 

 relates to infection on pond pine. Hedgcock and Siggers reported that 

 pond pine, with 38% infection, was almost as susceptible as slash pine 

 (41% infection). Only one collection in our study, #645 from coastal 

 South Carolina where pond pine is native, produced an appreciable amount 

 of infection (7%) . This is considerably less than Hedgcock and Siggers 

 reported and may possibly indicate pathogenic variability on the part of 

 the fungus, difference in resistance on the part of the host, or simply 

 a difference in inoculation techniques . 



Kais and Snow- indicated some differences in levels of pathogenicity 

 between collections of C. fusiforme on different strains of slash pine. 

 Overall, however, C. fusiforme seems relatively uniform in its patho- 

 genicity. 



The two collections of C. quevcuum., one from jack and one from 

 Virginia pine, produced contrasting infection results on several of the 

 pine species tested. The Virginia pine collection (#648) produced galls 

 on 43% of the Virginia pine seedlings and on 1% of the jack pine; the 

 jack pine collection (#671) produced 70% infection on jack pine and none 

 on Virginia pine. This demonstrates the existence of distinct physio- 

 logic races of this organism. The differential reactions of these pine 

 hosts are of essentially the same magnitude as those of the wheat rust 

 differentials used to distinguish between the numerous races of Puocinia 

 graminis Pers . f. sp. tvitici Eriks. and Henn . The 2 pine hosts involved 

 are, of course, different species. In the case of wheat stem rust, 

 5 different species of Iriticum make up the differential varieties, so 

 again the situation is comparable. 



In addition to the differential responses on the jack and Virginia 

 pine, there were several sharp differences in the amount of infection on 

 some other species. Sand pine, for example, was quite susceptible (54%) 

 to collection #648, but was highly resistant (1%) to collection #671. 

 Loblolly pine was only slightly susceptible (20%) to collection #648 and 

 highly resistant (1%) to #671. Slash pine was also slightly susceptible 

 to collection i 648 (17%), but quite susceptible (54%) to # 6"1 . However, 

 the infections on slash pine caused by both C. quercuum collections were 

 atypical, producing a very small, round gall with copious resinosis. 



1 Q, 



ee Zais and Snob), these -proceedings. 



